Gaseous NGL (natural gas liquid) not being cryogenic, after vaporization tends to include considerable entrained liquid natural gas. The presence of such entrained liquids undermines the qualitative accuracy of the energy value of the measured gas. This problem has been exacerbated with the substantial development of NGL recovery from fracking.
Unlike a typical gas obtained from conventional sources, NGL introduces a new analytical complication due to the presence of heavy hydrocarbons (e.g. those composed of more than five carbon atoms and generally in liquid form) not present in streams obtained from traditional gas wells. For example, widegrades containing a substantial range of methane through C5 and heavier components, e.g., asphalts, a material with vaporization temperatures in the 300-400° F. (148-204° C.) range, may cool sufficiently to cause phase separation and resulting component non-uniformity depending on when the measurement is taken depending on where in the phase transition curve. It is the stratification of lighters and heavier constituents that creates such deviations and skews the analysis. Reliquification following vaporization before analysis creates an even more serious scenario. Because the large majority of GCs do not operate properly at temperatures below 150° F. (65° C.) and above 180° F. (82° C.) and pressures under 10 psig, if a liquid is introduced into a conventional gas chromatograph (GC), it floods and disables the analyzer.
Many processing facilities for NGL rely on multiple and redundant, up to twenty-five gas chromatograph, and moisture analyzers, most being disposed midstream. It is well known that such analyzers, particularly gas chromatographs, are expensive—costing up to $50,000 each. In the event of flooding of a GC, it must be shut down and rebuilt or even replaced. In addition to the costs of processing interruptions occasioned by such shut downs, substantial maintenance, labor and equipment costs also result.
Many sample takeoff and conditioning units incorporate a liquid block feature to avoid the flooding problem. It has been found, however, that disposing of such a conventional liquid block, removes temperature and pressure limitations within the conditioning cabinet to thereby permit complete vaporization of the significantly increased “liquid heavies”.